This invention relates to die cutting and in particular to a method of making, and the tools for making, clear dies having internal sidewalls that diverge from the cutting edge, out of bar stock.
Cutting dies have been used for a long time to cut pieces from sheet material. Many of these dies are not clear, that is they have internal crossbracing to stiffen the die and help it maintain its shape. However, these cross braces prevent the cut pieces from passing through the dies. Thus, the cut pieces had to be removed, or stripped, from the die between cutting operatings. This impedes the productivity of the die and requires special equipment and/or extra labor to service the die. Various stripping devices have been developed, but they require further equipment to handle the cut pieces removed from the dies.
It is desirable to have the cut pieces pass through the die, but this is difficult even in a clear die without internal cross-bracing because the vertical die walls do not readily permit passage of the cut pieces. To alleviate this problem, the internal side walls of the die can be made so that they diverge from the cutting edge, permitting the cut pieces to travel through the die and out where they can be conveniently collected without interfering with the operation of the die. The difficulty with this solution has been in manufacturing a clear die to the desired shape while maintaining the diverging configuration of the sidewalls. Such dies have been made by forging or casting, but the dies are extremely expensive. An inexpensive method of making a die of any shape where the sidewalls diverge from the cutting edge was not available, and thus such dies were not available to many industries where they could be used to great advantage. For example, in the shoe industry as many as 40 different dies are needed to make soles for the entire size range in just one style. The cost of making clear diverging dies has thus been exhorbitant.
The present invention is a method of making, and the tools for making, clear dies having sidewalls that diverge from the cutting edge, out of barstock. The resulting dies differ from prior dies, even prior dies that may have been constructed from bar stock, because they are clear, without any internal bracing, yet they have diverging sidewalls facilitating the throughput of cut pieces. Because the die is made from bar stock it is more quickly and inexpensively fabricated than prior art dies with diverging sidewalls.
The dies are made from thin bar stock with wide sides, the bar stock having an internal side that is flat, for the interior of the die, and an external side that is flat for a portion and then tapers inwardly to form a cutting edge. The method comprises cutting a section of bar stock to the approximate perimeter of the die, and, starting at one end, successively bending and advancing the section according to a pattern to shape the die. The bends are made with one of two sets of male and female tools, a first set for making internal bends toward the center of the die, and a second set for making external bends away from the center of the die.
The first set of tools comprises a female tool having two lands for supporting the external side of the bar stock, the lands sloping so that the cutting edge on the bar stock points away from the female tool, the lands converging toward the cutting edge on the bar stock. The lands are separated by a vertical tapering slot. The first set of tools also comprises a male tool that has a bending-edge aligned with the slot in the female tool and sloped generally in the same direction as the lands. The bending-edge is straight and engages the internal side of the bar stock. The male tool is operated to push the bar stock into the slot, bending the bar stock between the lands. The diverging configuration of the die walls is maintained because the bar stock is held at an angle as it is bent. Further, consistent with the desired diverging configuration of the walls, the bend sharpens toward the cutting edge because of the converging configuration of the lands.
The second set of tools comprises a female tool having two lands for supporting the internal side of the bar stock, the lands sloping so that the cutting edge on the bar stock points toward the female tool, the lands converging toward the cutting edge on the bar stock. The lands are separated by a vertical tapering slot. The second set of tools also comprises a male tool that has a bending-edge aligned with a slot in the female tool and sloped generally in the same direction as the lands. The bending-edge engages the external side of the bar stock. The male tool is operated to push the bar stock into the slot in the female tool, bending the bar stock between the lands. The diverging configuration of the die walls is maintained because the bar stock is held at an angle as it is bent. Further, consistent with the diverging configuration of the die walls, the bend sharpens toward the cutting edge because of the converging configuration of the lands.
The new method further comprises trimming the section upon completion of the shaping operations, and joining the ends together to form a complete die. The cutting edge of the die can then be sharpened and the opposite edge can be ground flat to eliminate any irregularities. The die can also be heat treated, if desired.